Medical image processing device, method for operating the same, and endoscope system

ABSTRACT

First RGB image signals are inputted. Color difference signals Cr and Cb are calculated from the first RGB image signals. In a feature space formed by the color difference signals Cr and Cb, a first process and a second process are performed. In the first process, coordinates which correspond to the first, second, and third observation areas are moved in a parallel manner such that the coordinates which correspond to the second observation area are moved to a reference area that contains the origin point. In the second process, the coordinates which correspond to the first observation area and the coordinates which correspond to the third observation area are moved away from each other.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority under 35 U.S.C. §119 to JapanesePatent Application No. 2014-133391, filed Jun. 27, 2014. Each of theabove application(s) is hereby expressly incorporated by reference, inits entirety, into the present application.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a medical image processing device forproducing an image in which a difference in color between a normal siteand a lesion site is enhanced, a method for operating a medical imageprocessing device, and an endoscope system.

2. Description Related to the Prior Art

In medical fields, diagnoses utilizing endoscope systems have beenwidely performed. The endoscope system comprises a light source device,an endoscope, and a processor device. In the endoscope system,illumination light is applied from the endoscope to a region of interest(object) and the object under the illumination light is imaged with animaging element of the endoscope. An image of the object is displayed ona monitor based on image signals obtained by imaging the object. Adoctor detects the presence or absence of a lesion while observing theimage displayed on the monitor.

It is easy to detect a lesion (e.g. protrusion from mucosal surface)which significantly differs from a normal site (normal portion) in shapeand size. However, with regard to a lesion which is similar to thenormal portion in shape and size, the lesion is detected based on adifference in color from that of the normal portion. It is extremelydifficult to detect the lesion in a case where the lesion is in itsearly stage and there is little difference in color between the lesionand the normal portion. In Japanese Patent No. 3228627, a difference incolor between the normal portion and the lesion is made clearly visibleby a process to further move a portion which is displaced from areference value of blood volume (hemoglobin index) away from thereference value. It is known that gastric (stomach) cancer causesatrophy of gastric mucosa (mucous membrane layer of the stomach), whichmakes the color of the gastric mucosa to fade. For this reason, there isa difference in color between the atrophic mucosa and the normal mucosa.The stomach cancer is diagnosed by observing the difference in colorbetween the suspected lesion and the normal portion with an endoscope.“ABC method (ABC screening)” is recommended by the authorized nonprofitorganization “Japan Research Foundation of Prediction, Diagnosis andTherapy for Gastric Cancer”.

In advanced stages of atrophy (for example, groups C or D in the ABCscreening), the difference in color between the normal portion and theatrophic portion is clear, so that it is easy to detect the atrophicportion. However, in intermediate stages (for example, groups B and C inthe ABC screening), there is little difference in color between theatrophic portion and the normal portion. Therefore it is difficult todetect the atrophic portion based only on the difference in color. It isnecessary to enhance the difference in color between the atrophicportion and the normal portion to facilitate the detection of theatrophic portion even if there is little difference in color betweenthem.

Note that the difference in color between the atrophic portion and thenormal portion may be enhanced using a method described in JapanesePatent No. 3228627. However, the color of the atrophic portion isaffected not only by the blood volume but also by factors other than theblood volume. Therefore it is difficult to enhance the difference incolor between the atrophic portion and the normal portion with the useof the method described in the Japanese Patent No. 3228627.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a medical imageprocessing device for producing an image in which a difference in colorbetween an abnormal portion such as an atrophic portion with atrophicgastric mucosa and a normal portion is enhanced, a method for operatinga medical image processing device, and an endoscope system.

A medical image processing device according to the present inventioncomprises an input processing unit, a color information obtainingsection, and a first movement processor. The input processing unitperforms an input process of a first color image signal. The colorinformation obtaining section obtains two or more pieces of colorinformation from the first color image signal. The first movementprocessor moves coordinates within a feature space from first, second,and third observation areas so as to move the coordinates from aspecific observation area to a reference area defined in the featurespace and moves the coordinates within the feature space from the twoobservation areas, other than the specific observation area, out of thethe first to third observation areas, to be away from each other. Thefeature space is formed by the two or more pieces of color information.The specific observation area is one of the first to third observationareas. Objects of interest are distributed in the first, second, andthird observation areas.

It is preferred that the feature space is a Cb-Cr space formed by colordifference signals Cr and Cb, being the two or more pieces of colorinformation, or an ab space formed by color components a* and b*, beingthe two or more pieces of color information, of CIE Lab space. It ispreferred that, within the feature space, the first movement processormoves the coordinates in a parallel manner from the first, second, andthird observation areas so as to move the coordinates from the specificobservation area to the reference area and changes angles of thecoordinates located in the two observation areas, other than thespecific observation area, out of the first to third observation areasso as to move the coordinates from the two observation areas to be awayfrom each other. It is preferred that the reference area includes anorigin point of the feature space but excludes the two observation areasother than the specific observation area.

It is preferred that the two or more pieces of color information are hueH and saturation S, and the feature space is an HS space formed by thehue H and the saturation S. It is preferred that, within the HS space,the first movement processor moves the coordinates in a parallel mannerin a saturation direction from the first, second, and third observationareas so as to move the coordinates from the specific observation areato the reference area and moves the coordinates in a hue direction fromthe two observation areas, other than the specific observation area, outof the first to third observation areas, to be away from each other. Itis preferred that the reference area includes an origin point of the HSspace but excludes the two observation areas other than the specificobservation area.

It is preferred that the medical image processing device furthercomprises a second movement processor for moving the coordinates withinthe feature space from the second observation area to the reference areawhile the coordinates in the first and third observation areas aremaintained unchanged and for moving the coordinates within the featurespace from the third observation area while the coordinates in the firstobservation area are maintained unchanged.

It is preferred that the feature space is Cb-Cr space formed by colordifference signals Cr and Cb, being the two or more pieces of colorinformation, or an ab space formed by color components a* and b*, beingthe two or more pieces of color information, of CIE Lab space. It ispreferred that, in the feature space, the second movement processorchanges a radial coordinate of the coordinates in the second observationarea to move the coordinates from the second observation area to thereference area while the coordinates in the first and third observationareas are maintained unchanged, and changes an angle of the coordinatesin the third observation area to move the coordinates from the thirdobservation area while the coordinates in the first observation area aremaintained unchanged and while the coordinates moved from the secondobservation area are maintained in the reference area.

It is preferred that the two or more pieces of color information are hueH and saturation S, and the feature space is an HS space formed by thehue H and the saturation S. It is preferred that, within the HS space,the second movement processor moves the coordinates in a saturationdirection from the second observation area to the reference area whilethe coordinates in the first and third observation areas are maintainedunchanged and moves the coordinates in a hue direction from the thirdobservation area while the coordinates in the first observation area aremaintained unchanged and while the coordinates moved from the secondobservation area are maintained in the reference area. It is preferredthat the reference area includes an origin point of the HS space butexcludes the first observation area and the third observation area.

It is preferred that the medical image processing device furthercomprises a color image signal converter and a brightness adjuster. Thecolor image signal converter converts the two or more pieces of colorinformation, which have been processed through the first movementprocessor or the second movement processor, into a second color imagesignal. The brightness adjuster adjusts a pixel value of the secondcolor image signal based on first brightness information obtained fromthe first color image signal and second brightness information obtainedfrom the second color image signal.

It is preferred that the first color image signal is three color imagesignals. It is preferred that, in the feature space, a differencebetween the first observation area and the second observation area of acase where at least one of the three color image signals is a narrowbandsignal is greater than a difference between the first observation areaand the second observation area of a case where all of the three colorimage signals are broadband signals, or a difference between the firstobservation area and the third observation area of the case where atleast one of the three color image signals is a narrowband signal isgreater than a difference between the first observation area and thethird observation area of the case where all of the three color imagesignals are broadband signals.

An endoscope system comprises the above-described medical imageprocessing device according to the present invention and a display unit.The display unit displays a first special image obtained from two ormore pieces of color information processed by the first movementprocessor and a second special image obtained from two or more pieces ofcolor information processed by the second movement processor.

A method for operating a medical image processing device comprises aninput processing step, a color information obtaining step, and amovement processing step. In the input processing step, an inputprocessing unit performs an input process of a first color image signal.In the color information obtaining step, a color information obtainingsection obtains two or more pieces of color information from the firstcolor image signal. In the movement processing step, a first movementprocessor moves coordinates within a feature space from first, second,and third observation areas so as to move the coordinates from aspecific observation area to a reference area defined in the featurespace and moves the coordinates within the feature space from the twoobservation areas, other than the specific observation area, out of thefirst to third observation areas, to be away from each other. Thefeature space is formed by the two or more pieces of color information.The specific observation area is one of the first to third observationareas. Objects of interest are distributed in the first, second, andthird observation areas.

According to the present invention, an image in which a difference incolor between an abnormal portion (e.g. an atrophic portion with anatrophic gastric mucosa) and a normal portion is enhanced is produced.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects and advantages of the present invention willbe more apparent from the following detailed description of thepreferred embodiments when read in connection with the accompanieddrawings, wherein like reference numerals designate like orcorresponding parts throughout the several views, and wherein:

FIG. 1 is an external view of an endoscope system according to a firstembodiment;

FIG. 2 is a block diagram illustrating functions of the endoscopeaccording to the first embodiment;

FIG. 3 is a graph illustrating emission spectrums of violet light V,blue light B, green light G, and red light;

FIG. 4 is a block diagram illustrating functions of a first specialimage processor;

FIG. 5 is an explanatory view illustrating a first process for a signalratio space;

FIG. 6 is a graph illustrating distribution of the first to thirdobservation areas after the first process for the signal ratio space;

FIG. 7 is a graph illustrating distribution of the first to thirdobservation areas after the first process of a case where the featurespace is ab space;

FIG. 8 is a block diagram illustrating functions of the special imageprocessor used for the ab space;

FIG. 9 is an explanatory view illustrating a second process for thesignal ratio space;

FIG. 10 is a graph illustrating a region to which the angle θ in theangle changing region R1 is moved;

FIG. 11 is a graph representing a relationship between the angle θ andthe angle Eθ which is obtained after the second process (for the signalratio space);

FIG. 12 is a graph illustrating distribution of the first to thirdobservation areas after the second process for the signal ratio space;

FIG. 13 is a graph illustrating distribution of the first to thirdobservation areas after the second process for the ab space;

FIG. 14 is a block diagram illustrating functions of the second specialimage processor;

FIG. 15 is an explanatory view illustrating a third process for thesignal ratio space;

FIG. 16 is a graph illustrating a relationship between radial coordinater and radial coordinate Er;

FIG. 17 is a graph illustrating distribution of the first to thirdobservation areas after a third process for the signal ratio space;

FIG. 18 is a graph illustration distribution of the first to thirdobservation areas after the third process for the ab space;

FIG. 19 is an explanatory view illustrating a fourth process for thesignal ratio space;

FIG. 20 is a graph illustrating a region to which an angle θ in an anglechanging region R3 is moved;

FIG. 21 is a graph illustrating a relationship between angle θ and angleEθ obtained after a fourth process for the signal ratio space;

FIG. 22 is a graph illustrating distribution of the first to thirdobservation areas after the fourth process for the signal ratio space;

FIG. 23 is a graph illustrating distribution of the first to thirdobservation areas after the fourth process for the ab space;

FIG. 24 is an image view of a monitor which displays a first specialimage and a second special image at a time;

FIG. 25 is a flowchart illustrating steps of the present invention;

FIG. 26 is a block diagram illustrating functions of a first specialimage processor used for Cb-Cr space formed by Cr and Cb;

FIG. 27 is an explanatory view illustrating a positional relationshipamong the first, second, and third observation areas in the Cb-Cr space;

FIG. 28 is an explanatory view illustrating a first process in the Cb-Crspace;

FIG. 29 is an explanatory view illustrating a second process in theCb-Cr space;

FIG. 30 is a block diagram illustrating functions of a second specialimage processor used for the Cb-Cr space;

FIG. 31 is an explanatory view illustrating a third process in the Cb-Crspace;

FIG. 32 is an explanatory view illustrating a fourth process in theCb-Cr space;

FIG. 33 is a block diagram illustrating functions of the first specialimage processor in HS space formed by H (hue) and S (saturation);

FIG. 34 is an explanatory view illustrating a positional relationshipamong the first, second, and third observation areas in the HS space;

FIG. 35 is an explanatory view illustrating a first process in the HSspace;

FIG. 36 is an explanatory view illustrating a second process in the HSspace;

FIG. 37 is a block diagram illustrating functions of the second specialimage processor used for the HS space;

FIG. 38 is an explanatory view illustrating a third process for the HSspace;

FIG. 39 is an explanatory view illustrating a fourth process for the HSspace;

FIG. 40 is a block diagram illustrating functions of an endoscope systemaccording to the second embodiment;

FIG. 41 is a graph illustrating an emission spectrum white light:

FIG. 42 is a graph illustrating an emission spectrum of special light;

FIG. 43 is a block diagram illustrating functions of an endoscope systemaccording to a third embodiment;

FIG. 44 is a plan view illustrating a rotary filter;

FIG. 45 is a block diagram illustrating functions of a capsule endoscopesystem;

FIG. 46 is a graph illustrating emission spectrums of violet light V,blue light B, and red light R, which differ from those illustrated inFIG. 3;

FIG. 47 is a block diagram illustrating functions of the first specialimage processor in which a two-dimensional LUT is used; and

FIG. 48 is an explanatory view illustrating positions of the second andthird observation areas in the feature space in the case where the firstB image signal is a narrowband signal and positions of the second andthird observation areas in the feature space in the case where the firstB image signal is a broadband signal.

DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment

As illustrated in FIG. 1, an endoscope system 10 of a first embodimentcomprises an endoscope 12, a light source device 14, a processor device16, a monitor (display unit) 18, and a console 19. The endoscope 12 isconnected optically to the light source device 14, and electrically tothe processor device 16. The endoscope 12 comprises an insertion section12 a to be inserted into a body cavity, a control handle unit 12 bprovided at the proximal end of the insertion section 12 a, a flexibleportion 12 c, and a distal portion 12 d. The distal portion 12 d iscoupled to the flexible portion 12 c, which is provided on the distalside of the insertion section 12 a. The flexible portion 12 c is bent byoperating an angle knob 12 e of the control handle unit 12 b. The distalportion 12 d is directed to a desired direction by bending the flexibleportion 12 c.

The control handle unit 12 b is provided with the angle knob 12 e and amode switch (SW) 13 a. The mode SW 13 a is operated to switch among fourmodes: a normal mode, a first special mode, and a second special mode,and a simultaneous display mode. In the normal mode, a normal image isdisplayed on the monitor 18. The first special mode is used to observe aboundary between an atrophic portion (damaged portion) and a normalportion. The atrophic portion refers to a portion, of gastric mucosa(mucous membrane layer of the stomach), with atrophy (shrinkage inlinings of stomach) caused by a lesion such as stomach cancer. In thefirst special mode, a first special image is displayed on the monitor18. The second special mode is used to observe a difference in colorbetween the atrophic portion and the normal portion. In the secondspecial mode, a second special image is displayed on the monitor 18. Thesimultaneous display mode is used to observe the boundary between theatrophic portion and the normal portion and the difference in colorbetween the atrophic portion and the normal portion at a time. In thesimultaneous display mode, the first and second special images aredisplayed simultaneously or at a time on the monitor 18.

The processor device 16 is electrically connected to the monitor 18 andthe console 19. The monitor 18 outputs and displays image informationand the like. The console 19 functions as a UI (user interface), whichreceives input operation such as setting a function. Note that anexternal storage unit (not shown) for recording the image informationand the like may be connected to the processor device 16.

As illustrated in FIG. 2, the light source device 14 comprises a V-LED(Violet Light Emitting Diode) 20 a, a B-LED (Blue Light Emitting Diode)20 b, a G-LED (Green Light Emitting Diode) 20 c, an R-LED (Red LightEmitting Diode) 20 d, a source controller 21 for controlling the LEDs 20a to 20 d, and a combiner 23. The combiner 23 combines the optical pathsof four colors of light from the four colors of LEDs 20 a to 20 dtogether. The light combined by the combiner 23 is applied to the objectin a body cavity through a light guide (LG) 41 and a light lens 45. Thelight guide 41 extends inside the insertion section 12 a. Note that anLD (Laser Diode) may be used in place of the LED.

As illustrated in FIG. 3, the V-LED 20 a generates violet light V havinga wavelength range of 380 to 420 nm and the center wavelength 405±10 nm.The B-LED 20 b generates blue light B having a wavelength range of 420to 500 nm and the center wavelength 460±10 nm. The G-LED 20 c generatesgreen light G having a wavelength range of 480 to 600 nm. The R-LED 20 dgenerates red light R having a wavelength range of 600 to 650 nm and thecenter wavelength 620-630 nm.

In each of the normal mode, the first special mode, the second specialmode, and the simultaneous display mode, the source controller 21 mayturn on the V-LED 20 a, the B-LED 20 b, the G-LED 20 c, and the R-LED 20d. In this case, the mixture of the violet light V, the blue light B,the green light G, and the red light R is applied to the object. In thenormal mode, the source controller 21 controls the LEDs 20 a to 20 d tomake a light quantity ratio among the violet light V, the blue light B,the green light G, and the red light R to be Vc:Bc:Gc:Rc. In the firstand second special modes and the simultaneous display mode, the sourcecontroller 21 controls the LEDs 20 a to 20 d to make the light quantityratio among the violet light V, the blue light B, the green light G, andthe red light R to be Vs:Bs:Gs:Rs.

As illustrated in FIG. 2, the light guide 41 is incorporated in theendoscope 12 and a universal code that connects the endoscope 12, thelight source device 14, and the processor device 16. The light guide 41transmits the light combined by the combiner 23 to the distal portion 12d of the endoscope 12. Note that a multimode fiber may be used as thelight guide 41. For example, a small-diameter fiber cable with the corediameter 105 μm, the clad diameter 125 μm, and the outer diameter φ0.3to 0.5 mm (including a protection layer, being a jacket) may be used.

The distal portion 12 d of the endoscope 12 comprises an illuminationoptical system 30 a and an imaging optical system 30 b. The illuminationoptical system 30 a has the light lens 45. The light from the lightguide 41 is applied to the object through the light lens 45. The imagingoptical system 30 b has an objective lens 46 and an image sensor 48. Thelight reflected from the object is incident on the image sensor 48through the objective lens 46. Thereby a reflection image of the objectis formed on the image sensor 48.

The image sensor 48 is a color image sensor. The image sensor 48captures the reflection image of the object, and outputs an imagesignal. It is preferred that the image sensor 48 is a CCD (ChargeCoupled Device) image sensor, a CMOS (Complementary Metal-OxideSemiconductor) image sensor, or the like. The image sensor 48 used inthe present invention is a color image sensor for obtaining imagesignals of three colors, R (red), G (green), and B (blue), that is, aso-called RGB image sensor comprising R pixels with R filters, G pixelswith G filters, and B pixels with B filters.

Note that the image sensor 48 may be a so-called complementary colorimage sensor instead of the RGB image sensor. The complementary colorimage sensor has complementary color filters of C (cyan), M (magenta), Y(yellow), and G (green). In the case where the complementary color imagesensor is used, four colors (CMYG) of image signals are outputted. It isnecessary to convert the four colors (CMYG) of image signals into threecolors (RGB) of image signals through complementary color/primary colorconversion. Alternatively, the image sensor 48 may be a monochrome imagesensor with no color filters. In this case, it is necessary that thesource controller 21 allows emitting the blue light B, the green lightG, and the red light R in a time-division manner. It is also necessaryto add a synchronization process in processing the image signals.

The image signal outputted from the image sensor 48 is transmitted to aCDS/AGC circuit 50. The CDS/AGC circuit 50 performs correlated doublesampling (CDS) and automatic gain control (AGC) on the image signal,being an analog signal. The image signal which has passed through theCDS/AGC circuit 50 is converted into a digital image signal by an A/Dconverter 52. The A/D converted digital image signal is inputted to theprocessor device 16.

The processor device 16 comprises a receiver 53, a DSP (Digital SignalProcessor) 56, a noise remover 58, an image processing selector 60, anormal image processor 62, a special image processor 64, and a videosignal generator 66. The receiver 53 receives the digital RGB imagesignals from the endoscope 12. The R image signal corresponds to thesignals outputted from the R pixels of the image sensor 48. The G imagesignal corresponds to the signals outputted from the G pixels of theimage sensor 48. The B image signal corresponds to the signals outputtedfrom the B pixels of the image sensor 48.

The DSP 56 performs various types of signal processing (defectcorrection process, offset processing, gain correction process, linearmatrix processing, gamma conversion process, demosaicing process, andthe like) on the image signal received. In the defect correctionprocess, signals from defective pixels in the image sensor 48 arecorrected. In the offset processing, dark current components are removedfrom the RGB image signals which have been subjected to the defectcorrection process. Thereby an accurate zero level is set. In the gaincorrection process performed after the offset processing, a signal levelis adjusted or corrected by multiplying the RGB image signals by aspecific gain. After the gain correction process, the RGB image signalsare subjected to the linear matrix processing to increase colorreproducibility. Thereafter, brightness and saturation are adjusted orcorrected through the gamma conversion process. After the linear matrixprocessing, the RGB image signals are subjected to the demosaicingprocess (also referred to as equalization process) in which colorsignal(s) lacking in each pixel is generated by interpolation. Owing tothe demosaicing process, each pixel has three colors (RGB) of signals.

The DSP 56 performs gamma correction and the like on the RGB imagesignals. Thereafter, the noise remover 58 removes noise from the RGBimage signals through a noise removing process (for example, movingaverage method or median filter method). Then, the RGB image signals aretransmitted to the image processing selector 60. Note that “inputprocessing unit” of the present invention corresponds to theconfiguration comprising the receiver 53, the DSP 56, and the noiseremover 58.

In the case of the normal mode set by operating the mode SW 13 a, theimage processing selector 60 transmits the RGB image signals to thenormal image processor 62. In the case of the first special mode, thesecond special mode, or the simultaneous display mode, the imageprocessing selector 60 transmits the RGB image signals to the specialimage processor 64.

The normal image processor 62 performs color conversion process, colorenhancement process, and structure enhancement process on the RGB imagesignals. In the color conversion process, the digital RGB image signalsare subjected to 3×3 matrix processing, tone conversion process,three-dimensional LUT process, and the like. Thereby the digital RGBimage signals are converted into the color-converted RGB image signals.Next, the color-converted RGB image signals are subjected to varioustypes of color enhancement processes. The color-enhanced RGB imagesignals are subjected to the structure enhancement process (e.g. spatialfrequency enhancement and the like). The structure-enhanced RGB imagesignals are inputted as the RGB image signals of the normal image fromthe normal image processor 62 to the video signal generator 66.

The special image processor 64 operates when the mode is set to thefirst special mode, the second special mode, or the simultaneous displaymode. The special image processor 64 comprises a first special imageprocessor 64 a for producing a first special image, a second specialimage processor 64 b for producing a second special image, and a thesimultaneous display image processor 64 c for producing a special imageused for displaying the first and second special images at a time. Thefirst special image processor 64 a does not produce the second specialimage. The second special image processor 64 b does not produce thefirst special image. The first special image processor 64 a, the secondspecial image processor 64 b, and the simultaneous display imageprocessor 64 c will be described in detail below. The RGB image signalsof the first special image, the second special image, or the specialimage for simultaneous display, which are generated in the special imageprocessor 64, are inputted to the video signal generator 66.

The video signal generator 66 converts the RGB image signals, which areinputted from the normal image processor 62 or the special imageprocessor 64, into a video signal to be displayed as an image on themonitor 18. Based on the video signal, the monitor 18 displays thenormal image, the first special image, or the second special image, orthe first and second special images at a time.

As illustrated in FIG. 4, the first special image processor 64 acomprises an inverse gamma converter 70, a log converter 71, a signalratio calculator 72, a parallel movement section 73, a polar coordinateconverter 74, an angle expansion/compression unit 75, a Cartesiancoordinate converter 76, an RGB converter 77, a structure enhancer 78,an inverse log converter 79, and a gamma converter 80. The first specialimage processor 64 a also comprises a brightness adjuster 82 between theRGB converter 77 and the structure enhancer 78. Note that the “firstmovement processor” of the present invention corresponds toconfiguration which includes the parallel movement section 73 and theangle expansion/compression unit 75 in the first special image processor64 a.

The inverse gamma converter 70 performs inverse gamma conversion on theinputted RGB channels. The RGB image signals after the inverse gammaconversion are linearly-changing RGB signals which change linearlyrelative to reflectance from the object. Owing to this, a proportion ofthe signal components related to various types of biological informationincreases in the RGB image signals. Note that the linearly-changing Rimage signal is referred to as a first R image signal. Thelinearly-changing G image signal is referred to as a first G imagesignal. The linearly-changing B image signal is referred to as a first Bimage signal.

The log converter 71 performs log conversion of each of the first RGBimage signals (which correspond to “first color image signal” of thepresent invention). Thereby, log-converted R image signal (log R),log-converted G image signal (log G), and log-converted B image signal(log B) are obtained. The signal ratio calculator 72 (which correspondsto a “color information obtaining section” of the present invention)performs difference processing (log G−log B=log G/B=−log(B/G)) based onthe log-converted G image signal and the log-converted B image signal.Thereby, the B/G ratio is calculated. The B/G ratio refers to −log(B/G)with the “−log” omitted. The G/R ratio is calculated by differenceprocessing (log R−log G=log R/G=−log(G/R)) based on the log-converted Rimage signal and the log-converted G image signal. The G/R ratio refersto −log(G/R) with the “−log” omitted in a manner similar to the B/Gratio.

Note that the B/G ratio and the G/R ratio are calculated with respect tothe pixels in the same positions in the B image signal, the G imagesignal, and the R image signal. The B/G ratio and the G/R ratio arecalculated for each pixel. The B/G ratio correlates with a blood vesseldepth (distance between the mucosal surface and a position of a specificblood vessel), so that the B/G ratio varies with the blood vessel depth.The G/R ratio correlates with the blood volume (hemoglobin index), sothat the G/R ratio varies with the blood volume.

The parallel movement section 73 performs the first process for thesignal ratio space. In the first process, the parallel movement section73 translates or moves the coordinates in a parallel manner from acertain area or range, based on the B/G and G/R ratios calculated by thesignal ratio calculator 72. The polar coordinate converter 74 performsthe conversion into the radial coordinate r and the angular coordinate θbased on the B/G and G/R ratios (coordinates) which have been moved inthe parallel manner by the parallel movement section 73. The polarcoordinate converter 74 performs the conversion into the radialcoordinate r and the angular coordinate θ for each pixel. The angleexpansion/compression unit 75 performs a second process (for the signalratio space). In the second process, the angle expansion/compressionunit 75 expands or compresses the angular coordinate B based on theradial coordinate r and the angular coordinate θ which have beensubjected to the first process (for the signal ratio space) and thepolar coordinate conversion performed by the polar coordinate converter74. The first and second processes (for the signal ratio space) will bedescribed below in detail.

The Cartesian coordinate converter 76 converts the expanded orcompressed radial coordinate r and angular coordinate θ (the radialcoordinate r and angular coordinate θ which have been subjected to thesecond process for the signal ratio space by the angleexpansion/compression unit 75), into Cartesian coordinates. Thereby theradial coordinate r and angular coordinate θ are converted back into theB/G ratio and the G/R ratio. The RGB converter 77 (which corresponds toa “color image signal converter” of the present invention) uses at leastone of the first RGB image signals, which are outputted from the inversegamma converter 70, to convert the B/G and G/R ratios, which have passedthrough the Cartesian coordinate converter 76, into the second RGB imagesignals (which correspond to “second color image signals” of the presentinvention). To convert the B/G ratio into a second B image signal, theRGB converter 77 performs arithmetic operations based on the B/G ratioand the first G image signal of the first RGB image signals, forexample. To convert the G/R ratio into a second R image signal, the RGBconverter 77 performs arithmetic operations based on the G/R ratio andthe first G image signal of the first RGB image signals, for example.The RGB converter 77 outputs the first G image signal as a second Gimage signal, without any conversion.

The brightness adjuster 82 adjusts or corrects the pixel values of thesecond RGB image signals based on the first RGB image signals and thesecond RGB image signals. A reason for adjusting the pixel values of thesecond RGB image signals by the brightness adjuster 82 is as follows.The brightness of the second RGB image signals, which are obtained bythe expansion and compression processes of the color region performed bythe parallel movement section 73 and the angle expansion/compressionunit 75, may become significantly different from the brightness of thefirst RGB image signals. The brightness adjuster 82 adjusts the pixelvalues of the second RGB image signals to make the brightness of thesecond RGB image signals after the brightness adjustment equal to thebrightness of the first RGB image signals.

The brightness adjuster 82 comprises a first brightness informationcalculator 82 a and a second brightness information calculator 82 b. Thefirst brightness information calculator 82 a calculates first brightnessinformation Yin based on the first RGB image signals. The secondbrightness information calculator 82 b calculates second brightnessinformation Yout based on the second RGB image signals. The firstbrightness information calculator 82 a calculates the first brightnessinformation Yin with the use of an arithmetic expression “kr×pixel valueof first R image signal+kg×pixel value of first G image signal+kb×pixelvalue of first B image signal”. The second brightness informationcalculator 82 b calculates the second brightness information Yout withthe use of an arithmetic expression similar to that described above, ina manner similar to the first brightness information calculator 82 a.After calculating the first brightness information Yin and the secondbrightness information Yout, the brightness adjuster 82 performsarithmetic operations based on the following expressions (E1) to (E3),thereby adjusting the pixel values of the second RGB image signals.

R*=pixel value of second R image signal×Yin/Yout   (E1)

G*=pixel value of second G image signal×Yin/Yout   (E2)

B*=pixel value of second B image signal×Yin/Yout   (E3)

Note that “R*” denotes the second R image signal after the brightnessadjustment. “G*” denotes the second G image signal after the brightnessadjustment. “B*” denotes the second B image signal after the brightnessadjustment. Each of “kr”, “kg”, and “kb” is an arbitrary constant withina range from 0 to 1.

The structure enhancer 78 performs the structure enhancement process onthe second RGB image signals after the brightness adjustment in thebrightness adjuster 82. The structure enhancement process may befrequency filtering or the like. The inverse log converter 79 performsinverse log conversion on the second RGB image signals which have passedthrough the structure enhancer 78. Thereby the second RGB image signalswith antilogarithmic pixel values are obtained. The gamma converter 80performs the gamma conversion on the RGB image signals which have passedthrough the inverse log converter 79. Thereby the second RGB imagesignals with the tone suitable for an output device (e.g. the monitor18) are obtained. The RGB image signals, which have passed through thegamma converter 80, are transmitted as the RGB image signals of thefirst special image to the simultaneous display image processor 64 c orthe video signal generator 66.

As illustrated in FIG. 5, the first process (for the signal ratio space)performed by the parallel movement section 73 will be described belowusing a feature space (signal ratio space), being a two-dimensionalcolor space formed by the B/G ratio (vertical axis) and the G/R ratio(horizontal axis). In the first process (for the signal ratio space),first, an average value (Xa, Ya) of the coordinates in a secondobservation area, in which atrophic mucosa damaged or shrunk by atrophicgastritis is distributed, in the signal ratio space is calculated. Next,all of the coordinates corresponding to the second observation area, allof the coordinates corresponding to a first observation area, in whichthe normal mucosa is distributed, and all of the coordinatescorresponding to a third observation area, which is located beneath theatrophic mucosa damaged or shrunk by the atrophic gastritis and in whichdeep blood vessels seen through the atrophic mucosa are distributed, aremoved in a parallel manner by the magnitude of the average value (Xa,Ya) in the negative direction with respect to the vertical direction andin the negative direction with respect to the horizontal direction.Thereby, as illustrated in FIG. 6, the coordinates corresponding to thesecond observation area move to the reference area that contains theorigin point of the signal ratio space, and the coordinatescorresponding to the first and third observation areas move toward thereference area while the positional relationship with the coordinatescorresponding to the second observation area is maintained. Thereference area refers to a region with low saturation, which excludesthe first and third observation areas which have been subjected to thefirst process (for the signal ratio space).

Note that in the case of the feature space (ab space) formed by a* andb* (color components a* and b*, being the color information, in a CIELab space, the same hereinafter), which are obtained by the Labconversion of the first RGB image signals performed by a Lab converter(which corresponds to the “color information obtaining section” of thepresent invention) 83 (see FIG. 8), all of the coordinates correspondingto the first observation area, all of the coordinates corresponding tothe second observation area, and all of the coordinates corresponding tothe third observation areas are moved in a parallel manner by theaverage value of the coordinates which correspond to the secondobservation area so that the coordinates which correspond to the secondobservation area are moved to the reference area (see FIG. 7). Here, inFIG. 7, “the first to third observation areas depicted with dottedlines” represent the positions of the first to third observation areasin the ab space before the first process (for the ab space). “The firstto third observation areas depicted with solid lines” represent thepositions of the first to third observation areas in the ab space afterthe first process.

Note that, in the case where the first process (for the ab space) isperformed with the use of a* and b*, a special image processor 84 (seeFIG. 8) is used. Unlike the special image processor 64 a, the specialimage processor 84 is not provided with the inverse gamma converter 70,the log converter 71, the signal ratio calculator 72, the inverse logconverter 79, and the gamma converter 80. Instead, the special imageprocessor 84 comprises the Lab converter 83, which corresponds to the“color information obtaining section” of the present invention. Thecomponents, other than those described above, of the special imageprocessor 84 are the same as or similar to the components of the specialimage processor 64 a.

The Lab converter 83 converts the first RGB image signals into L, a*,and b* through the well-known Lab conversion. The “L” is transmitted tothe RGB converter 77 and the brightness adjuster 82. The “a*” and “b*”are transmitted to the polar coordinate converter 74. The RGB converter77 converts the “a*” and which have passed through the Cartesiancoordinate converter 76, and the “L” into the second RGB image signals.The first brightness information calculator 82 a of the brightnessadjuster 82 converts the “L”, which is transmitted from the Labconverter 83, into a luminance signal Y with the use of a predeterminedconversion equation. The converted luminance signal Y is referred to asthe first brightness information Yin. The second brightness informationcalculator 82 b calculates the second brightness information Yout fromthe second RGB image signals. The brightness adjuster 82 uses the firstbrightness information Yin and the second brightness information Yout toadjust the pixel values of the second RGB image signals. Note that themethod for calculating the second brightness information Yout and themethod for adjusting the pixel values of the second RGB image signalsare the same as or similar to those of the special image processor 64 a.

As illustrated in FIG. 9, in the second process (for the signal ratiospace) performed by the angle expansion/compression unit 75, the angle θof the coordinates (point) P1 in an angle changing region R1 is changedwhile the angle θ of the coordinates (point) outside the angle changingregion R1 is not changed. The angle changing region R1 is set to includethe first observation area and the third observation area. Note that, inthe second process (for the signal ratio space), the radial coordinate rof the coordinates (point) inside the angle changing region R1 is notchanged.

In the angle changing region R1, a first center line CL1 is set betweenthe first observation area and the third observation area. The firstcenter line CL1 has an angle θc. The coordinates (point) with an angle(angular coordinate) θ which is smaller than the angle θc in the anglechanging region R1 are rotated in the clockwise direction A1 while thecoordinates (point) with an angle (angular coordinate) θ which isgreater than the angle θc in the angle changing region R1 are rotated inthe counter clockwise direction A2. Note that, in the case where theangle θ is within a range R1 x extending from the first center line CL1,it is preferred to perform the expansion process for changing the angleθ at an angle change rate Wx, which is greater than “1”. In the casewhere the angle θ is within a range R1 y outside the range R1 x, it ispreferred to perform the compression process for changing the angle θ atan angle change rate Wy, which is less than “1”. It is preferred to movethe coordinates, which are located in the angle changing region R1,within a region extending ±90° (degrees) from the first center line CL1(e.g. a region P extending from “270°+θc” to “θc+90°” in the case wherethe “positive” horizontal axis is 0° and an angle is expressed in degreefrom 0° to 360° (see FIG. 10)) through the second process (for thesignal ratio space). Note that in a case where the angle change rate is“1”, the angle θ does not change when subjected to the process forchanging the angle θ.

Here, an angle change rate is represented by the inclination of astraight line “L1”, being the tangent line of a curve CV1. The curve CV1depicts the relationship between angles θ and Eθ. The inclination of thestraight line L1 is greater than “1” in the range R1 x. On the otherhand, the inclination of the straight line L1 is less than “1” in therange R1 y (see FIG. 11). The inclination of the straight line L1outside the angle changing region R1 is “1” (see FIG. 11).

By the second process (for the signal ratio space), as illustrated inFIG. 11, the angle θ which is less than the angle θc in the anglechanging region R1 is changed to an angle Eθ which is smaller than theangle θ. The angle θ greater than the angle θc is changed to the angleEθ which is greater than the angle θ. The angle θ outside the anglechanging region R1 is changed to the angle Eθ which is equivalent to theangle θ (identical transformation).

Thereby, as illustrated in FIG. 12, most of the coordinatescorresponding to the first observation area are moved to the secondquadrant of the signal ratio space and most of the coordinatescorresponding to the third observation area are moved to the fourthquadrant of the signal ratio space while the coordinates correspondingto the second observation area are maintained in the reference area.Thus, the coordinates corresponding to the first observation area andthe coordinates corresponding to the third observation area are locatedin the different quadrants in the signal ratio space. The first specialimage obtained after the second process (for the signal ratio space)clearly shows the boundary between the atrophic portion, which includesatrophic mucosa and the deep blood vessels seen through the atrophicmucosa, and the normal portion with the normal mucosa.

Note that in the case where the feature space is the ab space, asillustrated in FIG. 13, the second process (for the ab space) moves mostof the coordinates which correspond to the first observation area to thesecond quadrant of the ab space and most of the coordinates whichcorrespond to the third observation area to the fourth quadrant of theab space while the coordinates which correspond to the secondobservation area are maintained within the reference area. It ispreferred that the brightness adjuster 82 adjusts the pixel values ofthe second RGB image signals obtained after the first and secondprocesses (for the ab space). The method for adjusting the second RGBimage signals is the same as or similar to that described above.

As illustrated in FIG. 14, the second special image processor 64 b hasthe same or similar configuration as that of the first special imageprocessor 64 a. However, the second special image processor 64 b isprovided with the radial coordinate expansion/compression unit 81 inplace of the parallel movement section 73. The process performed by theangle expansion/compression unit 75 in the second special imageprocessor 64 b differs from the second process (for the signal ratiospace) performed by the first special image processor 64 a. Note thatthe “second movement processor” of the present invention corresponds tothe configuration which includes the radial coordinateexpansion/compression unit 81 and the angle expansion/compression unit75.

The radial coordinate expansion/compression unit 81 performs the thirdprocess (for the signal ratio space), in which the radial coordinate ris changed based on the radial coordinate r and the angle θ, which havebeen converted by the polar coordinate converter 74. Referring to FIG.15, the third process is described using the signal ratio space. In thethird process, a radial coordinate r of the coordinates (point) P2located within the radial coordinate changing region R2 is changed whilea radial coordinate r of the coordinates (point) located outside of theradial coordinate changing region R2 is not changed. In the radialcoordinate changing region R2, the radial coordinate r takes a valuebetween “rA” and “rB” and the angle θ takes a value between “θA” and“θB” (rA<rB, θA<θB). The radial coordinate changing region R2 is set toinclude the second observation area, in which atrophic mucosa (damagedmucosal tissue) caused by the atrophic gastritis (damaged stomachlining) is distributed, and exclude the first observation area and thethird observation area. In the first observation area, normal mucosa isdistributed. The third observation area is located beneath the atrophicmucosa caused by the atrophic gastritis, and deep blood vessels aredistributed in the third observation area. The deep blood vessels in thethird observation area appear through the atrophic mucosa as the atrophyprogresses.

Note that, in the third process for the signal ratio space, the angularcoordinate (angle) θ of the coordinates (point) in the radial coordinatechanging region R2 is not changed. In the third process, it is preferredto perform an expansion process on the radial coordinate r in the casewhere the radial coordinate r is in a range of “rp” to “rB” and acompression process on the radial coordinate r in the case where theradial coordinate r is in a range of “rA” to “rp”. In the expansionprocess, the radial coordinate r is changed at a radial coordinatechange ratio Vx, which is greater than “1”. In the compression process,the radial coordinate r is changed at a radial coordinate change ratioVy, which is less than 1. Note that, in the case where the radialcoordinate change ratio is “1”, the length of the radial coordinate rdoes not change even if the process for changing the radial coordinate ris performed.

Here, a radial coordinate change rate is represented by the inclinationof a straight line “L2”, being the tangent line of a curve CV2. Thecurve CV2 depicts the relationship between the radial coordinate r andthe radial coordinate Er. The inclination of the straight line L2 isgreater than “1” in the range of “rp” to “rB”. On the other hand, theinclination of the straight line L2 is less than “1” in the range of“rA” to “rp” (see FIG. 16). The inclination of the straight line L2outside the radial coordinate changing region R2 is “1” (see FIG. 16).

By the third process (for the signal ratio space), as illustrated inFIG. 16, the radial coordinate r in the radial coordinate changingregion R1 is changed to the radial coordinate Er which is smaller thanthe radial coordinate r. The radial coordinate r located outside theradial coordinate changing region R2 is changed to the radial coordinateEr which is equivalent to the radial coordinate r (identicaltransformation). Thereby, as illustrated in FIG. 17, only thecoordinates which correspond to the second observation area are moved tothe reference area that contains the origin point while the coordinateswhich correspond to the first observation area and the coordinates whichcorrespond to the third observation area are maintained unchanged. Notethat the saturation in the special image is decreased by moving thecoordinates which correspond to the second observation area.

Note that, in the case where the feature space is the ab space, asillustrated in FIG. 18, the third process (for the ab space) moves onlythe coordinates which correspond to the second observation area to thereference area that contains the origin point while the coordinateswhich correspond to the first observation area and the coordinates whichcorrespond to the third observation area are maintained unchanged.

The angle expansion/compression unit 75 of the second special imageprocessor 64 b performs a fourth process (for the signal ratio space).In the third process, the angle expansion/compression unit 75 changesthe angle θ based on the radial coordinate r and the angle θ which areobtained after the third process (for the signal ratio space), to movethe coordinates which correspond to the third observation area while thecoordinates which correspond to the first observation area aremaintained unchanged. In the fourth process (for the signal ratiospace), as illustrated in FIG. 19, the angle θ of coordinates (point) P3within the angle changing region R3 is changed while the angle θ ofcoordinates outside the angle changing region R3 is not changed. Theangle changing region R3 is set to include the third observation areaand exclude the first observation area. Note that in the fourth process(for the signal ratio space), the radial coordinate r of the coordinatesin the angle changing region R3 is not changed.

A second center line CL2 is set between the first observation area andthe third observation area in the angle changing region R3. The secondcenter line CL2 is set at an angle θd. The coordinates having the angleθ which is less than or equal to the angle θd in the angle changingregion R3 are rotated in the clockwise direction. Note that, in the casewhere the angle θ is within a range R3 x extending from the secondcenter line CL2, it is preferred to perform the expansion process forchanging the angle θ at an angle change rate Wx, which is greater than“1”. In the case where the angle θ is within a range R3 y outside therange R3 x, it is preferred to perform the compression process forchanging the angle θ at an angle change rate Wy, which is less than “1”.It is preferred to move the coordinates, which are located in the anglechanging region R3, within a region extending −90° (degrees) from thesecond center line CL2 (e.g. a region Q extending from “270°+θd” to “θd”in the case where the “positive” horizontal axis is 0° and an angle isexpressed in degree from 0° to 360° (see FIG. 20)) through the fourthprocess (for the signal ratio space). Note that in a case where theangle change rate is “1”, the angle θ does not change when subjected tothe process for changing the angle θ.

Here, an angle change rate is represented by the inclination of astraight line “L3”, being the tangent line of a curve CV3. The curve CV3depicts the relationship between angles θ and Eθ. The inclination of thestraight line L3 is greater than “1” in the range R3 x. On the otherhand, the inclination of the straight line L3 is less than “1” in therange R3 y (see FIG. 21). The inclination of the straight line L3outside the angle changing region R3 is “1” (see FIG. 21).

By the fourth process (for the signal ratio space), as illustrated inFIG. 21, the angle θ which is located in the angle changing region R3 ischanged to the angle Eθ which is smaller than the angle θ. The angle θoutside the angle changing region R3 is changed to the angle Eθ which isequivalent to the angle θ (identical transformation).

Thereby, as illustrated in FIG. 22, most of the coordinatescorresponding to the third observation area are moved to the fourthquadrant of the signal ratio space while the coordinates correspondingto the second observation area are maintained in the reference area andwhile the coordinates corresponding to the first observation area aremaintained unchanged. By moving the coordinates which correspond to thethird observation area from the first quadrant to the fourth quadrant,the hue is changed in the signal ratio space. Thus, the coordinatescorresponding to the first observation area, the coordinatescorresponding to the second observation area, and the coordinatescorresponding to the third observation area are moved away from eachother.

Note that, as illustrated in FIG. 23, in the case where the featurespace is the ab space, most of the coordinates corresponding to thethird observation area are moved to the fourth quadrant of the ab spaceby the fourth process (for the ab space) while the coordinatescorresponding to the second observation area are maintained in thereference area and while the coordinates corresponding to the firstobservation area are maintained unchanged. It is preferred that thebrightness adjuster 82 adjusts the pixel values of the second RGB imagesignals obtained after the third and fourth processes (for the abspace). The method for adjusting the pixel values of the second RGBimage signals is the same or similar to that described above.

In the second special image obtained after the fourth process (for thesignal ratio space), the color of the normal portion is maintained inthe display while the color of the atrophic mucosa of the atrophicportion with the atrophic gastritis is displayed in faded colors and thedeep blood vessels seen through the atrophic mucosa are displayed in acolor which corresponds to the atrophic state. Thus, the second specialimage displayed shows the gastric mucosa infected with atrophicgastritis in actual colors, so that the difference in color between thenormal portion and the atrophic portion is clear.

Based on the first special image produced by the first special imageprocessor 64 a and the second special image produced by the secondspecial image processor 64 b, the simultaneous display image processor64 c produces a special image for simultaneous display. As illustratedin FIG. 24, the monitor 18 displays the first special image on one sideof the monitor 18 and the second special image on the other side of themonitor 18, based on the special image for simultaneous display. In thefirst special image, a boundary between the normal portion and theatrophic portion is clear enough to facilitate finding the position ofthe atrophic portion or the like. However, the normal portion isdisplayed in pseudo color, which is not the actual color of the gastricmucosa (mucous membrane layer of the stomach). The pseudo color gives adoctor an unnatural impression. In the second special image, as comparedwith the first special image, the boundary between the normal portionand the atrophic portion is clear to some extent, but the color of thenormal portion is displayed in actual color of the stomach, so that thesecond special image gives a doctor a natural impression. Thesimultaneous display of the first and second special images allows adoctor to detect the boundary of the normal portion and the atrophicportion while checking the color of the normal portion.

Hereinafter, referring to a flowchart in FIG. 25, an operation of thepresent invention is described. First, the mode is set to the normalmode. The insertion section 12 a of the endoscope 12 is inserted intothe body cavity. After the distal portion 12 d of the insertion section12 a reached the stomach, the mode SW 13 a is operated to switch fromthe normal mode to the first or second special mode. Note that the modeis switched to the simultaneous display mode in the case where a doctorperforms a diagnosis of the atrophic gastritis while observing both ofthe first and second special images.

Based on the RGB image signals obtained after the mode is switched tothe first or second special mode, the signal ratio calculator 72calculates the B/G ratio and the G/R ratio. Then, in a case where themode is set to the first special mode, the first process (for the signalratio space) is performed. The signal ratio space is formed by the B/Gratio and the G/R ratio. In the first process, the coordinatescorresponding to the first observation area, the coordinatescorresponding to the second observation area, and the coordinatescorresponding to the third observation area are moved in a parallelmanner such that the coordinates corresponding to the second observationarea are moved to the reference area. In the first observation area, thenormal mucosa is distributed. In the second observation area, atrophicmucosa damaged (or shrunk) due to the atrophic gastritis is distributed.In the third observation area, the deep blood vessels, which are locatedbeneath the atrophic mucosa and seen through the atrophic mucosa, aredistributed.

Next, in either of the first and second special modes, the B/G ratio andthe G/R ratio are converted into a radial coordinate r and an angle θ bythe polar coordinate conversion. In the first special mode, the secondprocess for the signal ratio space is performed based on the radialcoordinate r and an angle θ obtained after the first process for thesignal ratio space and the polar coordinate conversion. In the secondprocess, the coordinates corresponding to the first observation area andthe coordinates corresponding to the third observation area are movedaway from each other. The radial coordinate r and an angle θ obtainedafter the second process are converted into Cartesian coordinatesthrough Cartesian coordinate conversion. The first special image isproduced based on the B/G ratio and the G/R ratio obtained after theCartesian coordinate conversion. The first special image is displayed onthe monitor 18.

In the second special mode, the third process (for the signal ratiospace) is performed. In the third process, the coordinates correspondingto the second observation area are moved to the reference area while thecoordinates corresponding to the first and third observation areas aremaintained unchanged, based on the radial coordinate r and the angle θobtained after the polar coordinate conversion. Then the fourth process(for the signal ratio space) is performed. In the fourth process, thecoordinates corresponding to the third observation area are moved whilethe coordinates corresponding to the first observation area aremaintained unchanged, based on the radial coordinate r and the angle θobtained after the third process. The radial coordinate r and the angleθ obtained after the fourth process are converted into Cartesiancoordinates through the Cartesian coordinate conversion. A secondspecial image is produced based on the B/G and G/R ratios obtained afterthe Cartesian coordinate conversion. The second special image isdisplayed on the monitor 18.

Note that, in the simultaneous display mode, the simultaneous display isnot limited to that of the first special image and the second specialimage. For example, the first special image and the normal image may bedisplayed simultaneously, or the second special image and the normalimage may be displayed simultaneously. In those cases, the normal imageand the special image are produced in the normal image processor 62 andthe special image processor 64, respectively, and displayed on themonitor 18 through the video signal generator 66.

In the simultaneous display mode, the first special image and a thirdspecial image may be displayed simultaneously. The third special imagerefers to an image which has not been subjected to any of the first tothird processes. The third special image is produced by a third specialimage processor (not shown) provided in the special image processor 64.Unlike the first special image processor 64 a, the third special imageprocessor is not provided with the parallel movement section 73, thepolar coordinate converter 74, the angle expansion/compression unit 75,the Cartesian coordinate converter 76, and the RGB converter 77. Otherthan those, the third special image processor is similar to the firstspecial image processor 64 a. Note that in the case of producing thethird special image, it is preferred that the light of each color isemitted with the light intensity of the violet light V greater thanthose of the blue light B, the green light G, and the red light R. Inthe third special image taken under the light of such emissionconditions, the surface blood vessels are enhanced while the excellentbrightness of the entire image is maintained.

Note that, in the above embodiment, the signal ratio calculator 72calculates the B/G ratio and the G/R ratio based on the first RGB imagesignals. The first to fourth processes are performed in the featurespace formed by the B/G ratio and the G/R ratio. Alternatively, two ormore pieces of color information which differ from the B/G ratio and theG/R ratio may be obtained. The first to fourth processes may beperformed in a feature space formed by the two or more pieces of colorinformation.

For example, color difference signals Cr and Cb may be obtained as thecolor information. The first to fourth processes may be performed in afeature space formed by the color difference signals Cr and Cb. In thecase where the first special image is produced by using the colordifference signals Cr and Cb, a first special image processor 94 aillustrated in FIG. 26 is used. Unlike the first special image processor64 a, the first special image processor 94 a is not provided with theinverse gamma converter 70, the log converter 71, the signal ratiocalculator 72, the inverse log converter 79, and the gamma converter 80.Instead, the first special image processor 94 a comprises aluminance/color difference signal converter 85. The components, otherthan those described above, of the first special image processor 94 aare the same as or similar to the components of the first special imageprocessor 64 a.

The luminance/color difference signal converter 85, which corresponds tothe “color information obtaining section” of the present invention,converts the first RGB image signals into the luminance signal Y and thecolor difference signals Cr and Cb. A well-known conversion equation isused for the conversion into the color difference signals Cr and Cb. Thecolor difference signals Cr and Cb are transmitted to the parallelmovement section 73. The luminance signal Y is transmitted to the RGBconverter 77 and the brightness adjuster 82. The RGB converter 77converts the color difference signals Cr and Cb, which have passedthrough the Cartesian coordinate converter 76, and the luminance signalY into the second RGB image signals. The brightness adjuster 82 adjuststhe pixel values of the second RGB image signals with the use of theluminance signal Y (the first brightness information Yin) and the secondbrightness information (the second brightness information Yout) which iscalculated by the second brightness information calculator 82 b. Notethat the method for calculating the second brightness information Youtand the method for adjusting the pixel values of the second RGB imagesignals are the same as or similar to those of the first special imageprocessor 64 a.

The first special image processor 94 a performs the first process andthe second process (for the Cb-Cr space) in the feature space(hereinafter referred to as the Cb-Cr space; the vertical axis: thecolor difference signal Cr, the horizontal axis: the color differencesignal Cb) to produce the first special image. In the Cb-Cr space, asillustrated in FIG. 27, the second observation area (denoted as “2”) isclosest to the origin point . The first and third observation areas(denoted as “1” and “3”, respectively) are located farther from theorigin point than is the second observation area. The first observationarea is located close to the horizontal axis Cb. The third observationarea is located close to the vertical axis Cr.

In the first process (for the Cb-Cr space), as illustrated in FIG. 28,the parallel movement section 73 performs processing to move all of thecoordinates corresponding to the first to third observation areas in aparallel manner such that the coordinates corresponding to the secondobservation area are moved to the reference area containing the originpoint of the Cb-Cr space. The parallel movement made by the parallelmovement section 73 is the same as or similar to that of the case of thesignal ratio space. The reference area refers to a region with lowchroma or saturation, excluding the first and third observation areaswhich have been subjected to the first process (for the Cb-Cr space).

Note that, in FIGS. 28 and 29, the areas before the first process (forthe Cb-Cr space) are depicted with dotted lines. The areas after thefirst process are depicted with solid lines. This also applies to thedrawings described below. Here, “1”, “2”, and “3” denote the first,second, and third observation areas, respectively (the samehereinafter).

In the second process (for the Cb-Cr space), as illustrated in FIG. 29,the angle expansion/compression unit 75 performs processing to move thecoordinates which correspond to the first observation area and thecoordinates which correspond to the third observation area away fromeach other while the coordinates which correspond to the secondobservation area are maintained in the reference area. The method formoving the coordinates which correspond to the first and thirdobservation areas are similar to that in the signal ratio space. Inother words, the coordinates are moved by the expansion or thecompression of the angle (angular coordinate).

In the case where the second special image is produced by using thecolor difference signals Cr and Cb, a second special image processor 94b (see FIG. 30) is used. Unlike the second special image processor 64 b,the second special image processor 94 b is not provided with the inversegamma converter 70, the Log converter 71, the signal ratio calculator72, the inverse Log converter 79, and the gamma converter 80. Instead,the second special image processor 94 b comprises the luminance/colordifference signal converter 85. Other than those, the components of thesecond special image processor 94 b are the same as or similar to thoseof the second special image processor 64 b. Note that the functions ofthe luminance/color difference signal converter 85, the RGB converter77, and the brightness adjuster 82 are the same as or similar to thoseof the first special image processor 94 a, so that the descriptionsthereof are omitted.

The second special image processor 94 b performs the third process andthe fourth process (for the Cb-Cr space) in the Cb-Cr space to producethe second special image. In the third process (for the Cb-Cr space), asillustrated in FIG. 31, the radial coordinate expansion/compression unit81 performs processing to move the coordinates which correspond to thesecond observation area to the reference area that contains the originpoint of the Cb-Cr space while the coordinates which correspond to thefirst observation area and the coordinates which correspond to the thirdobservation area are maintained unchanged. The method for moving thecoordinates which correspond to the second observation area is the sameas or similar to that in the signal ratio space. In other words, thecoordinates which correspond to the second observation area are moved byexpanding or compressing the radial coordinates.

As illustrated in FIG. 32, in the fourth process (for the Cb-Cr space),the angle expansion/compression unit 75 performs processing to move onlythe coordinates which correspond to the third observation area away fromthe coordinates which correspond to the first observation area while thecoordinates which correspond to the second observation area aremaintained within the reference area and while the coordinates whichcorrespond to the first observation area are maintained unchanged. Themethod for moving the coordinates which correspond to the thirdobservation area is the same as or similar to that in the case of thesignal ratio space, and performed by expanding or compressing the angle(angular coordinate).

The color information may be hue H and saturation S. The first to fourthprocesses may be performed in the feature space (HS space) formed by thehue H and the saturation S. In the case where the first special image isproduced by using the hue H and the saturation S, a first special imageprocessor 96 a (see FIG. 33) is used. Unlike the first special imageprocessor 64 a, the first special image processor 96 a is not providedwith the inverse gamma converter 70, the Log converter 71, the signalratio calculator 72, the parallel movement section 73, the polarcoordinate converter 74, the angle expansion/compression unit 75, theCartesian coordinate converter 76, the inverse Log converter 79, and thegamma converter 80. Instead, the first special image processor 96 acomprises an HSV converter 87, a first parallel movement section 90, anda second parallel movement section 91. The first and second parallelmovement sections 90 and 91 are placed between the HSV converter 87 andthe RGB converter 77. Other than those, the first special imageprocessor 96 a is the same as or similar to the first special imageprocessor 64 a.

The HSV converter 87, which corresponds to the “color informationobtaining section” of the present invention, converts the first RGBimage signals into hue H, saturation S, and value (lightness orbrightness) V. Well-known conversion equations are used for theconversion into the hue H, the saturation S, and the value V. The hue Hand the saturation S are transmitted to the first parallel movementsection 90. The value V is transmitted to the RGB converter 77. The RGBconverter 77 converts the hue H and the saturation S, which have passedthrough the second parallel movement section 91, and the value V, whichis transmitted from the HSV converter 87, into the second RGB imagesignals. The brightness adjuster 82 adjusts the pixel values of thesecond RGB image signals with the use of the first brightnessinformation Yin calculated by the first brightness informationcalculator 82 a and the second brightness information Yout calculated bythe second brightness information calculator 82 b. Note that the methodsfor calculating the first brightness information Yin and the secondbrightness information Yout and the method for adjusting the pixelvalues of the second RGB image signals are the same as or similar tothose of the first special image processor 64 a.

The first special image processor 96 a performs the first and secondprocesses (for HS space) to produce the first special image. Asillustrated in FIG. 34, in the HS space, the second observation area islocated lower than the first observation area in the saturationdirection (the vertical axis). The third observation area is located tothe right of the first and second observation areas in the hue direction(the horizontal axis). In the HS space, as illustrated in FIG. 35, inthe first process (for the HS space), the first parallel movementsection 90 moves all of the coordinates which correspond to the firstobservation area, all of the coordinates which correspond to the secondobservation area, and all of the coordinates which correspond to thethird observation area in a parallel manner so as to move thecoordinates which correspond to the second observation area to thereference area. Here, the reference area in the HS space is a regionwith low saturation and contains the origin point of the HS space, butexcludes the coordinates which correspond to the first and thirdobservation areas obtained after the first process (for the HS space).The first parallel movement section 90 translates or moves thecoordinates which correspond to the first observation area, thecoordinates which correspond to the second observation area, and thecoordinates which correspond to the third observation area downward in aparallel manner. The information related to the hue H and the saturationS obtained after the parallel movement is transmitted to the secondparallel movement section 91.

As illustrated in FIG. 36, in the second process (for the HS space)after the parallel movement by the first parallel movement section 90,the coordinates which correspond to the first observation area and thecoordinates which correspond to the third observation area are movedaway from each other in a parallel manner while the coordinates whichcorrespond to the second observation area are maintained in thereference area. The second parallel movement section 91 moves thecoordinates which correspond to the first observation area to the leftin the hue direction in a parallel manner, and moves the coordinateswhich correspond to the third observation area to the right in the huedirection in a parallel manner.

In the case where the second special image is produced by using the hueH and the saturation H, a second special image processor 96 b (see FIG.37) is used. The second special image processor 96 b is similar to thefirst special image processor 96 a, but differs from the first specialimage processor 96 a in that the second special image processor 96 b isprovided with a third parallel movement section 92, in place of thefirst parallel movement section 90, and a fourth parallel movementsection 93 in place of the second parallel movement section 91. Notethat the functions of the HSV converter 87, the RGB converter 77, andthe brightness adjuster 82 of the second special image processor 96 bare the same as or similar to those of the first special image processor96 a, so that the descriptions thereof are omitted.

The second special image processor 96 b performs the third and fourthprocesses (for the HS space) in the HS space to produce the secondspecial image. In the third process (for the HS space), as illustratedin FIG. 38, the third parallel movement section moves the coordinateswhich correspond to the second observation area downward in thesaturation direction in a parallel manner while the coordinates whichcorrespond to the first observation area and the coordinates whichcorrespond to the third observation area are maintained unchanged. Here,the reference area in the HS space is a region with low saturation whichcontains the origin point of the HS space, but excludes the coordinateswhich correspond to the first and third observation areas obtained afterthe first process (for the HS space). The information related to the hue(H) and the saturation (S) obtained after the parallel movement aretransmitted to the fourth parallel movement section 93.

In the fourth process (for the HS space), as illustrated in FIG. 39, thecoordinates which correspond to the third observation area are moved tothe right in the hue direction in a parallel manner while thecoordinates which correspond to the second observation area aremaintained in the reference area and while the coordinates whichcorrespond to the first observation area are maintained unchanged.

Second Embodiment

In the second embodiment, a laser and a phosphor are used, instead ofthe LEDs 20 a to 20 d of the four colors described in the firstembodiment, to illuminate the object. Other than that, the configurationis the same as or similar to that in the first embodiment.

As illustrated in FIG. 40, in the light source device 14 of an endoscopesystem 100 according to the second embodiment, a blue laser (denoted as445LD in FIG. 40) 104 and a blue-violet laser (denoted as 405LD in FIG.40) 106 are provided in place of the LEDs 20 a to 20 d of the fourcolors. The blue laser 104 emits blue laser beams with the centerwavelength 445±10 nm. The blue-violet laser 106 emits blue-violet laserbeams with the center wavelength 405±10 nm. The light emissions from thesemiconductor light emitting elements of the lasers 104 and 106 arecontrolled individually by a source controller 108. The light quantityratio between the light (laser beams) from the blue laser 104 and thelight (laser beams) from the blue-violet laser 106 is changed asdesired.

In the normal mode, the source controller 108 actuates the blue laser104. In the first special mode, the second special mode, or thesimultaneous display mode, the source controller 108 actuates andcontrols both the blue laser 104 and the blue-violet laser 106 such thatthe light-emission intensity of the blue laser beams is greater thanthat of the blue-violet laser beams. The laser beams emitted from eachof the lasers 104 and 106 are incident on the light guide (LG) 41through optical members (e.g. a condenser lens, an optical fiber, acombiner, and the like, all not shown).

Note that the full width at half maximum of the blue laser beams or theblue-violet laser beams is preferred to be in the order of ±10 nm.Broad-area type InGaN-based laser diodes may be used as the blue laser104 and blue-violet laser 106. The InGaNAs-based laser diodes and theGaNAs-based laser diodes may be used instead. A light emitting elementsuch as a light emitting diode may be used as the light source.

The illumination optical system 30 a is provided with the light lens 45and a phosphor 110 on which the blue laser beams or the blue-violetlaser beams from the light guide 41 are incident. The phosphor 110irradiated with the blue laser beams emits fluorescence. A part of theblue laser beams passes through the phosphor 110. The blue-violet laserbeams pass through the phosphor 110 without exciting the phosphor. Thelight from the phosphor 110 is applied to the object through the lightlens 45.

Here, in the normal mode, the blue laser beams are mostly incident onthe phosphor 110, so that the white light, being the combination of theblue laser beams and the fluorescence from the phosphor 110 excited bythe blue laser beams, is applied to the object as illustrated in FIG.41. In the first special mode, the second special mode, or thesimultaneous display mode, both the blue-violet laser beams and the bluelaser beams are incident on the phosphor 110, so that the special light,being the combination of the blue-violet laser beams, the blue laserbeams, and the fluorescence from the phosphor 110 excited by the bluelaser beams, is applied to the object as illustrated in FIG. 42.

Note that it is preferred to use the phosphor 110 containing two or moretypes of phosphor components (e.g. YAG-based phosphor, BAM(BaMgAl₁₀O₁₇),or the like) which absorb a part of the blue laser beams and emit lightof green to yellow colors. In the case where the semiconductor lightemitting elements are used as the excitation light sources for thephosphor 110 as described in this example, the high-intensity whitelight is provided with high light-emission efficiency, the intensity ofthe white light is controlled easily, and the variations in the colortemperature and chromaticity of the white light are small.

Third Embodiment

In the third embodiment, instead of the LEDs 20 a to 20 d of the fourcolors described in the first embodiment, a broadband light source (e.g.a xenon lamp) and a rotary filter are used to illuminate the object.Instead of the color image sensor 48, a monochrome image sensor is usedto image the object. The components other than those are the same as orsimilar to the components described in the first embodiment.

As illustrated in FIG. 43, in an endoscope system 200 of the thirdembodiment, a broadband light source 202, a rotary filter 204, and afilter switcher 205 are provided instead of the LEDs 20 a to 20 d in thelight source device 14. The imaging optical system 30 b is provided witha monochrome image sensor 206 with no color filter, in place of thecolor image sensor 48.

The broadband light source 202 is composed of a xenon lamp, a white LED,or the like, and emits the white light having the wavelength range fromblue to red. The rotary filter 204 comprises a normal filter 208provided on the inner side and a special filter 209 provided on theouter side (see FIG. 44). The filter switcher 205 shifts the rotaryfilter 204 in the radial direction. When the mode is set to the normalmode by the operation of the mode SW 13 a, the normal filter 208 of therotary filter 204 is inserted into the light path of the white light.When the mode is set to the first special mode, the second special mode,or the simultaneous display mode, the special filter 209 of the rotaryfilter 204 is inserted into the light path of the white light.

As illustrated in FIG. 44, the normal filter 208 comprises a B filter208 a, a G filter 208 b, and an R filter 208 c in the circumferentialdirection. The B filter 208 a transmits the blue light of the whitelight. The G filter 208 b transmits the green light of the white light.The R filter 208 c transmits the red light of the white light. In thenormal mode, the blue light, the green light, and the red light areapplied in this order to the object as the rotary filter 204 is rotated.

The special filter 209 comprises a Bn filter 209 a, a G filter 209 b,and an R filter 209 c in the circumferential direction. The Bn filter209 a transmits the blue narrowband light having a specific wavelengthrange of the white light. The G filter 209 b transmits the green lightof the white light. The R filter 209 c transmits the red light of thewhite light. In the special mode, the blue narrowband light, the greenlight, and the red light are applied in this order to the object as therotary filter 204 is rotated.

In the endoscope system 200, in the normal mode, the monochrome imagesensor 206 takes an image of the object every time the blue light, thegreen light, or the red light is applied to the object. Thereby, thethree colors (RGB) of image signals are obtained. The normal image isproduced based on the RGB image signals in a manner the same or similarto that in the first embodiment.

In the first special mode, the second special mode, or the simultaneousdisplay mode, the monochrome image sensor 206 takes an image of theobject every time the blue narrowband light, the green light, or the redlight is applied to the object. Thereby, the Bn image signal, the Gimage signal, and the R image signal are obtained. The first or secondspecial image is produced based on the Bn image signal, the G imagesignal, and the R image signal. The Bn image signal is used in place ofthe B image signal to produce the first or second special image. Otherthan that, the first or second special image is produced in a manner thesame as or similar to that of the first embodiment.

Fourth Embodiment

In a fourth embodiment, a swallow-type capsule endoscope is used,instead of the insertion-type endoscope 12 and the light source device14, to obtain the RGB image signals necessary for producing the normalimage, the first special image, or the second special image.

As illustrated in FIG. 45, a capsule endoscope system 300 according tothe fourth embodiment comprises a capsule endoscope 302, atransmission/reception antenna 304, a receiving device 306 for thecapsule endoscope 302, the processor device 16, and the monitor 18. Thecapsule endoscope 302 comprises an LED 302 a, an image sensor 302 b, animage processor 302 c, and a transmission antenna 302 d. Note that theprocessor device 16 is the same as or similar to the one used in thefirst embodiment. In the fourth embodiment, a mode switch (SW) 308 isprovided to switch among the normal mode, the first special mode, thesecond special mode, and the simultaneous display mode.

The LED 302 a emits white light. Inside the capsule endoscope 302, twoor more LEDs 302 a are provided. Here, it is preferred that the LED 302a is a white light LED which comprises a blue light source and aphosphor which converts wavelengths of light from the blue light sourceinto fluorescence. An LD (laser diode) may be used instead of the LED.The object is illuminated with the white light from the LED 302 a.

The image sensor 302 b is a color image sensor. The image sensor 302 btakes an image of the object illuminated with the white light andoutputs the RGB image signals. Here, it is preferred that the imagesensor 302 b is a CCD (Charge Coupled Device) image sensor or a CMOS(Complementary Metal-Oxide Semiconductor) image sensor. In the imageprocessor 302 c, the RGB image signals outputted from the image sensor302 b are subjected to a process for converting them into signals whichare to be transmitted through the transmission antenna 302 d. The RGBimage signals, which have passed through the image processor 302 c, aretransmitted wirelessly from the transmission antenna 302 d to thetransmission/reception antenna 304.

The transmission/reception antenna 304 is affixed to the subject's body,and receives the RGB image signals from the transmission antenna 302 d.The transmission/reception antenna 304 wirelessly transmits the receivedRGB image signals to the receiving device 306 for the capsule endoscope302. The receiving device 306 is connected to the receiver 53 of theprocessor device 16, and transmits the RGB image signals, which havebeen received from the transmission/reception antenna 304, to thereceiver 53.

Note that, in the above embodiments, the four colors of light with theemission spectrums illustrated in FIG. 3 are used by way of example. Theemission spectrums are not limited to this example. For example, asillustrated in FIG. 46, the green light G and the red light R may havethe same spectrums as those illustrated in FIG. 3. The violet light Vsmay have the center wavelength 410 to 420 nm in a wavelength rangeslightly shifted to a longer wavelength side than that of the violetlight V in FIG. 3. The blue light Bs may have the center wavelength 445to 460 nm in a wavelength range slightly shifted to a shorter wavelengthside than that of the blue light B in FIG. 3. Note that, in the aboveembodiments, the first process is performed based on the B/G and G/Rratios by the first special image processor 64 a. After the firstprocess, the B/G ratio and the G/R ratio are converted into the radialcoordinate r and the angular coordinate θ through the polar coordinateconversion. Then, the second process is performed based on the radialcoordinate r and the angular coordinate θ converted. Thereafter, theradial coordinate r and the angular coordinate θ are converted back intothe B/G ratio and the G/R ratio. Alternatively, as illustrated in FIG.47, a two-dimensional LUT 400 may be used to directly convert the B/Gand G/R ratios, without the polar coordinate conversion, into theprocessed B/G and G/R ratios which have been subjected to the first andsecond processes or the third and fourth processes.

Note that the two-dimensional LUT 400 stores the B/G and G/R ratios inassociation with the processed B/G and G/R ratios, which have beensubjected to the first and second processes (or third and fourthprocesses) performed based on the B/G and G/R ratios. Note that thesecond special image processor 64 b may use a two-dimensional LUT toperform the processing in a like manner. The first RGB image signalsoutputted from the inverse gamma converter 70 are inputted to thetwo-dimensional LUT 400. Alternatively, the first RGB image signals maybe inputted to the RGB converter 77, in a manner similar to the aboveembodiments.

Note that, in the above embodiments, the angle θ is changed in thesecond process to move the first observation area and the thirdobservation area away from each other. The first and third observationareas may be moved away from each other in a different way. For example,the radial coordinate r may be changed to move the first observationarea and the third observation area away from each other. Both theradial coordinate r and the angle θ may be changed to move the first tothird observation areas away from each other. In the fourth process, thecoordinates which correspond to the first observation area may bechanged while the coordinates which correspond to the third observationarea maintained unchanged.

Note that, in the above embodiments, the B/G ratio and the G/R ratio areobtained from the first RGB image signals. The signal ratio space isformed by the B/G ratio and the G/R ratio. In the case where the first Bimage signal is a narrowband signal obtained from narrowband light (forexample, the light with the half width of 20 nm or less) with a narrowwavelength range, the difference (distance) between the first and secondobservation areas and the difference (distance) between the first andthird observation areas in the signal ratio space increase as comparedwith those of the case where the first B image signal is a broadbandsignal obtained from broadband light (for example, the light with thehalf width of more than 20 nm) with a broad wavelength range. Here, theexamples of the “narrowband light” includes the “violet light V” and the“blue light B” of the first embodiment, the “blue laser beams” and the“blue-violet laser beams” of the second embodiment, “the blue narrowbandlight” of the third embodiment, and the “light from the blue lightsource” of the fourth embodiment.

In FIG. 48, “Xn” denotes the second observation area in the case wherethe first B image signal is the narrowband signal. “Xb” denotes thesecond observation area in the case where the first B image signal isthe broadband signal. “Xn” is located lower than the “Xb” in the signalratio space. “Yn” denotes the third observation area in the case wherefirst B image signal is the narrowband signal. “Yb” denotes the thirdobservation area in the case where the first B image signal is thebroadband signal. “Yn” is located lower than the “Yb” in the signalratio space.

As illustrated in FIG. 48, the difference D12 n between the averagevalue AXn of “Xn” and the average value AR1 of the first observationarea is greater than the difference D12 b between the average value AXbof “Xb” and the average value AR1 of the first observation area. Thedifference D13 n between the average value AYn of “Yn” and the averagevalue AR1 of the first observation area is greater than the differenceD13 b between the average AYb of “Yb” and the average value AR1 of thefirst observation area. As described above, in the case where the firstB image signal is the narrowband signal, the differences between thefirst observation area and the second and third observation areas aresignificant even before the process for expanding and compressing theradial coordinate. The difference in color between the normal portionand the atrophic portion is displayed more clearly by performing theprocess for expansion and compression on the first to third observationareas which are already distant from each other.

Note that, in the case where the first G image signal is the narrowbandsignal, the difference between the first observation area and the secondobservation area and the difference between the first observation areaand the third observation area are greater than those of the case wherethe first G image signal is the broadband signal in a manner similar tothe above. The narrowband signal is not limited to the first B imagesignal or the first G image signal described above. By using thenarrowband signal for at least one of the first RGB image signals, thedifference between the first and second observation areas and thedifference between the first and third observation areas are greaterthan those of the case where all of the first RGB image signals arebroadband signals. The examples of the “narrowband signal” includes theabove-described signal obtained from the narrowband light and a signalobtained by a spectral estimation process described in Japanese PatentLaid-Open Publication No. 2003-93336.

Note that the present invention is applicable to various types ofmedical image processing device in addition to the processor devicesincorporated in the endoscope systems described in the first to thirdembodiments and the capsule endoscope system described in the fourthembodiment.

Various changes and modifications are possible in the present inventionand may be understood to be within the present invention.

What is claimed is:
 1. A medical image processing device comprising: aninput processing unit for performing an input process of a first colorimage signal; a color information obtaining section for obtaining two ormore pieces of color information from the first color image signal; anda first movement processor for moving coordinates within a feature spacefrom first, second, and third observation areas so as to move thecoordinates from a specific observation area to a reference area definedin the feature space and for moving the coordinates from the twoobservation areas, other than the specific observation area, out of thefirst to third observation areas, to be away from each other, thefeature space being formed by the two or more pieces of colorinformation, the specific observation area being one of the first tothird observation areas, objects of interest being distributed in thefirst to third observation areas.
 2. The medical image processing deviceaccording to claim 1, wherein the feature space is a Cb-Cr space formedby color difference signals Cr and Cb, being the two or more pieces ofcolor information, or an ab space formed by color components a* and b*,being the two or more pieces of color information, of CIE Lab space. 3.The medical image processing device according to claim 2, wherein,within the feature space, the first movement processor moves thecoordinates in a parallel manner from the first, second, and thirdobservation areas so as to move the coordinates from the specificobservation area to the reference area and changes angles of thecoordinates located in the two observation areas, other than thespecific observation area, out of the first to third observation areasso as to move the coordinates from the two observation areas to be awayfrom each other.
 4. The medical image processing device according toclaim 2, wherein the reference area includes an origin point of thefeature space but excludes the two observation areas other than thespecific observation area.
 5. The medical image processing deviceaccording to claim 1, wherein the two or more pieces of colorinformation are hue H and saturation S, and the feature space is an HSspace formed by the hue H and the saturation S.
 6. The medical imageprocessing device according to claim 5, wherein, within the HS space,the first movement processor moves the coordinates in a parallel mannerin a saturation direction from the first, second, and third observationareas so as to move the coordinates from the specific observation areato the reference area and moves the coordinates in a hue direction fromthe two observation areas, other than the specific observation area, outof the first to third observation areas, to be away from each other. 7.The medical image processing device according to claim 5, wherein thereference area includes an origin point of the HS space but excludes thetwo observation areas other than the specific observation area.
 8. Themedical image processing device according to claim 1, further comprisinga second movement processor for moving the coordinates within thefeature space from the second observation area to the reference areawhile the coordinates in the first and third observation areas aremaintained unchanged and for moving the coordinates within the featurespace from the third observation area while the coordinates in the firstobservation area are maintained unchanged.
 9. The medical imageprocessing device according to claim 8, wherein the feature space isCb-Cr space formed by color difference signals Cr and Cb, being the twoor more pieces of color information, or an ab space formed by colorcomponents a* and b*, being the two or more pieces of color information,of CIE Lab space.
 10. The medical image processing device according toclaim 9, wherein, in the feature space, the second movement processorchanges a radial coordinate of the coordinates in the second observationarea to move the coordinates from the second observation area to thereference area while the coordinates in the first and third observationareas are maintained unchanged, and changes an angle of the coordinatesin the third observation area to move the coordinates from the thirdobservation area while the coordinates in the first observation area aremaintained unchanged and while the coordinates moved from the secondobservation area are maintained in the reference area.
 11. The medicalimage processing device according to claim 9, wherein the reference areaincludes an origin point of the feature space but excludes the firstobservation area and the third observation area.
 12. The medical imageprocessing device according to claim 8, wherein the two or more piecesof color information are hue H and saturation S, and the feature spaceis an HS space formed by the hue H and the saturation S.
 13. The medicalimage processing device according to claim 12, wherein, within the HSspace, the second movement processor moves the coordinates in asaturation direction from the second observation area to the referencearea while the coordinates in the first and third observation areas aremaintained unchanged and moves the coordinates in a hue direction fromthe third observation area while the coordinates in the firstobservation area are maintained unchanged and while the coordinatesmoved from the second observation area are maintained in the referencearea.
 14. The medical image processing device according to claim 12,wherein the reference area includes an origin point of the HS space butexcludes the first observation area and the third observation area. 15.The medical image processing device according to claim 8, furthercomprising: a color image signal converter for converting the two ormore pieces of color information, which have been processed through thefirst movement processor or the second movement processor, into a secondcolor image signal; and a brightness adjuster for adjusting a pixelvalue of the second color image signal based on first brightnessinformation obtained from the first color image signal and secondbrightness information obtained from the second color image signal. 16.The medical image processing device according to claim 1, wherein thefirst color image signal is three color image signals, and, within thefeature space, a difference between the first observation area and thesecond observation area of a case where at least one of the three colorimage signals is a narrowband signal is greater than a differencebetween the first observation area and the second observation area of acase where all of the three color image signals are broadband signals,or a difference between the first observation area and the thirdobservation area of the case where at least one of the three color imagesignals is a narrowband signal is greater than a difference between thefirst observation area and the third observation area of the case whereall of the three color image signals are broadband signals.
 17. Anendoscope system comprising: a medical image processing device accordingto claim 8; and a display unit for displaying a first special imageobtained from two or more pieces of color information processed by thefirst movement processor and a second special image obtained from two ormore pieces of color information processed by the second movementprocessor.
 18. A method for operating a medical image processing devicecomprising the steps of: performing an input process of a first colorimage signal with an input processing unit; obtaining two or more piecesof color information from the first color image signal with a colorinformation obtaining section; and moving coordinates within a featurespace from first, second, and third observation areas so as to move thecoordinates from a specific observation area to a reference area definedin the feature space and for moving the coordinates from the twoobservation areas, other than the specific observation area, out of thefirst to third observation areas, to be away from each other with afirst movement processor, the feature space being formed by the two ormore pieces of color information, the specific observation area beingone of the first to third observation areas, objects of interest beingdistributed in the first to third observation areas.